(537c) MOF-Supported Ionic Liquids As Efficient CO2 Adsorbents for Direct Air Capture

Metal-organic frameworks (MOFs) are promising carbon dioxide (CO₂) adsorbents because of their remarkably high surface area, controllable pore structures, and predictable functional groups. However, few research groups reported investigating ionic liquids (ILs) loaded on MOFs for direct air capture of CO₂. Herein, we prepared UiO-66 and treated it with methanol solvent and thermal activation. It showed ~3 times enhanced CO₂ capture capacity, from 15.1 mg/g to 45 mg/g at 1 bar of CO₂ pressure, and excellent recyclability. The methanol treatment efficiently removes the residual guest molecules, including N, N-dimethylformamide, dangling organic linkers, and their derivatives in the micropores of UiO-66 and improves the surface area, pore volume, and void fraction to enhance the CO₂ capacity. The molecular dynamic simulation also proved an excellent linear relationship between the surface areas, void fraction, and CO₂ capacity. When we load ionic liquids (e.g., [Na][Im]) on the methanol-treated UiO-66, the CO₂ capacity increases from 0.003 mmol/g to the maximum of 0.212 mmol/g at 0.4 mbar of CO₂ partial pressure. The [Na][Im]/UiO-66 displayed good recyclability. The kinetic studies showed that it followed a pseudo-first-order reaction rate model, and the reaction rate is closely related to the IL layer thickness. This work elucidates the IL/MOF activation mechanism and its applications in direct air capture of CO₂.